The present invention relates generally to waste heat recovery furnace systems which recover a portion of the waste heat generated during combustion, and specifically to regenerative combustion furnace systems in which the flow of gases is regeneratively cycled between two or more flow directions.
Waste heat recovery furnace systems typically involve the collection of a portion of the waste heat produced during combustion, and the application of the collected waste heat to combustion air being delivered to the combustion chamber.
Regenerative furnace system also involve the collection of the waste heat and the application of the collected waste heat to the combustion air, however, regenerative systems typically further involve the cycling of gas flow directions such that the heat collection and the respective heat transfer to incoming air occurs at the same location. For example, U.S. Pat. No. 3,814,223 to Webber and U.S. Pat. No. 4,528,012 to Sturgill each generally discloses regenerative furnace systems in which waste or exhaust gases are passed through a volume of bricks stacked in a staggered pattern (commonly called a "checker"), thus warming the bricks during one cycle, and subsequently combustion air is warmed as it passes through the checkers towards the combustion chamber during a second cycle. A typical regenerative system includes a pair of regenerators which cycle in cooperation with one another.
The regenerators in present regenerative furnace systems typically suffer from significant operational limitations due to variations in temperature within a single regenerator. During use localized areas of high temperature limit the potential of the furnace system and diminish the longevity of the equipment. Some regenerative systems include localized areas (often called "flues") within a regenerator which may help to equalize temperatures within a regenerator. For example, U.S. Pat. No. 3,196,086 to Wethly and U.S. Pat. No. 4,470,806 to Greco disclose regenerative systems involving valves and chambers, respectively. However, even though the flow of gases to and from the localized areas is regulated by valves, each of these disclosures teaches the adjustment of the respective valves in a uniform manner. This is still likely to result in temperature variations between the various localized areas (i.e., cross-flue thermal gradient) within a single regeneration. It is an object of the present invention to minimize for the cross-flue thermal gradient which occurs within a single regenerator.
Certain developments in regenerative systems, largely aimed at improving combustion efficiency, have resulted in the regulation of combustion air in a way which may reduce some of the cross-flue thermal gradient. For example, U.S. Pat. Nos. 4,874,311 to Gitman and 4,298,372 to Stover et al. each discloses the regulation of combustion air flow. The flow of exhaust or waste gas is not, however, directly regulated in either system. Since it is the waste gas which is likely to impose the greatest amount of cross-flue thermal gradient within a regenerator, such a system would not achieve the objectives of the present invention.
It is an object of the present invention to provide for a regenerative furnace system in which the flow of gases to and from at least one regenerator is regulated in such a way that the cross-flue thermal gradient as well as other differences and/or stresses are minimized.